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Gaylussite

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Gaylussite
Gaylussite - Lagunillas, Venezuela
General
CategoryCarbonate mineral
Formula
(repeating unit)
Na2Ca(CO3)2·5H2O
Strunz classification05.CB.35
Crystal systemMonoclinic 2/m
Identification
ColorColorless, white, yellow, and grey
Crystal habitTabular prismatic crystals also granular
Cleavageperfect [110]
FractureConchoidal, brittle
Mohs scale hardness2.5
Lustervitreous
Streakwhite
Specific gravity1.93 - 1.99
Optical propertiesBiaxial (-)
Refractive indexnα = 1.444 nβ = 1.516 nγ = 1.523
Birefringenceδ = 0.079
Solubilitydecomposes in water
Other characteristicsefflorescent
References[1][2][3]

Gaylussite is a carbonate mineral, a hydrated sodium calcium carbonate, formula Na2Ca(CO3)2·5H2O. It occurs as translucent, vitreous white to grey to yellow monoclinic prismatic crystals. It is an unstable mineral which dehydrates in dry air and decomposes in water.[1]

It is formed as an evaporite from alkali lacustrine waters. It also occurs rarely as veinlets in alkalic igneous rocks.[1] It was first described in 1826 for an occurrence in Lagunillas, Merida, Venezuela. It was named for French chemist Joseph Louis Gay-Lussac (1778–1850).[2]

The mineral has been recently reported from drill core in Lonar lake in central India.[4]

References

  1. ^ a b c Handbook of Mineralogy
  2. ^ a b Mindat
  3. ^ Webmineral
  4. ^ Anoop et al., Palaeoenvironmental implications of evaporative gaylussite crystals from Lonar Lake, central India, Journal of Quaternary Science, V., Issue 4, pp. 349–359, May 2013